1. Field of Invention
The present invention relates to a wheeled work vehicle that travels on tires.
2. Description of Related Art
In order to improve the comfort of the operator driving a work vehicle travelling on tires such as a wheeled hydraulic excavator, which has come to run at an increasingly high speed in recent years, Japanese Laid-Open Patent Publication No.S 62-110509, Japanese Laid-Open Patent Publication No. H 6-278438, Japanese Laid-Open Patent Publication No. H 7-125523 and Japanese Laid-Open Patent Publication No. H 7-132723, for instance, each disclose a work vehicle having a suspension mechanism provided between the body and an axle.
In the work vehicle disclosed in Japanese Laid-Open Patent Publication No. S62-110509 (hereafter referred to as prior art 1), two sets of hydraulic cylinders are provided at the two sides, i.e., on the left side and the right side of the body, the upper ends of the cylinder tubes and the lower ends of the cylinder rods are respectively linked to the body and the beam provided over the axle by using pins, and a long hole extending along the vertical direction is formed at the center of the body to link the upper center of the beam and the center of the body with a pin inserted at the long hole. The head chambers of the left hydraulic cylinder and the right hydraulic cylinder are made to communicate with each other via a restrictor. The head chambers of the left and right hydraulic cylinders are also connected to an accumulator via a pressure control valve. The line between the pressure control valve and the accumulator is connected to a hydraulic pump via a check valve which allows hydraulic oil to flow toward the accumulator. As a result, while the body moves vertically due to the contraction of the hydraulic cylinders when the wheels are subject to strong impact during travelling, the load is damped since the pressure control valve opens to communicate the hydraulic cylinders to the accumulator. If either of the left wheel or the right wheel is subject to an impact, the pressure oil from one of the hydraulic cylinders flows into the other hydraulic cylinder to rock the body.
In the work vehicle disclosed in Japanese Laid-Open Patent Publication No. H 6-278438 or Japanese Laid-Open Patent Publication No. H 7-132723 (hereafter referred to as prior art 2), double-acting hydraulic cylinders are mounted at the right side surface and the left side surface of the body with head chambers of the hydraulic cylinders connected with each other via a piping. A restrictor and an accumulator are provided in the middle of the piping and the lower ends of the cylinder rods of the hydraulic cylinders are individually linked to the axle of the work vehicle with pins. Thus, the vibration of the axle occurring during travelling is absorbed and damped to improve the comfort of the operator while travelling the vehicle.
Japanese Laid-Open Patent Publication No. H 7-125523 discloses a work vehicle (hereafter referred to as prior art 3) achieved by linking the upper ends of the cylinder tubes of one set of hydraulic cylinders and the lower ends of the cylinder rods respectively to the center of the body and the center of the axle with pins and linking the center of the axle and either the left side or the right side of the body with a link. In this vehicle, the bottom chamber of the hydraulic cylinder is connected to an accumulator via a restrictor. As a result, while the body moves in the vertical direction due to the contraction of the hydraulic cylinders if the wheels are subject to a strong impact during travelling, the load on the hydraulic cylinder communicating with the accumulator is attenuated.